Understanding the Question:
The question asks which plant family alfalfa (Medicago sativa) belongs to.
Key Concept:
Family assignment in botany rests on shared floral and fruiting structure, and legumes are recognized by pod-enclosed seeds, pea-shaped flowers and, often, nitrogen-fixing root nodules.
Checking Each Option:
Convolvulaceae covers twining vines like morning glory, nothing like alfalfa's low, leafy growth habit.
Liliaceae is a monocot family with parallel-veined leaves and three-part flowers, while alfalfa is a dicot with trifoliate leaves.
Acanthaceae plants carry tubular, two-lipped flowers, unlike alfalfa's small pea-type blooms.
Leguminosae fits because alfalfa forms seed pods, carries pea-shaped flowers, and partners with root-nodule bacteria to fix nitrogen, all defining traits of this family.
Final Answer:
Alfalfa belongs to the family Leguminosae.